This invention relates to a fuel controller for an internal combustion engine. More particularly, it relates to a fuel controller which can accurately measure the mass air flow rate into an engine using inexpensive equipment and control the fuel supply to the engine according to the measured flow rate.
In modern automotive engines, the air flow rate into the engine is closely monitored as an indication of the engine load, and the amount of fuel which is supplied to the engine by fuel injectors is controlled in accordance with the measured air flow rate so as to obtain an optimal air-fuel ratio.
There are two types of devices for measuring the mass air flow rate into an engine which are commonly employed in fuel control systems. One type is a mass air flow sensor which directly measures the mass air flow rate. The other type, which is referred to as a speed-density air flow sensor, employs an air pressure sensor and a temperature sensor which are mounted in the intake pipe of an engine. Based on the measured pressure and temperature of the intake air, a control unit calculates the mass air flow rate. A mass air flow rate sensor has excellent sensing accuracy but it is expensive, so fuel control system for inexpensive vehicles often use the more economical speed-density air flow sensor.
In a speed-density air flow sensor, the air pressure sensor is normally disposed in the air intake pipe downstream of the throttle valve of the engine. When the throttle valve opens or closes, the pressure which is sensed by the air pressure sensor fluctuates, and it is therefore necessary to take the average of the measured pressure. However, the time required for averaging increases the signal processing time, so a fuel controller employing a speed-density air flow sensor has a poor response speed and can not quickly adjust the fuel supply in accordance with changing operating conditions of the engine.